What are conductive bags?

Conductive bags is a transparent, usually pink, bag that protects sensitive electronics from damage caused by the harmful effects of static electricity. These bags are usually plastic and have a distinctive silvery color for metalized Mylar and other similar plastics and pink or black for poly bags. The poly bag way may also take the form of foam or bubble wrap, either as sheets or bags.

Question & Answer on conductive Bags

Question. What is the recommendation or guidelines in determining when conductive shielded bags are no longer any good, i.e. crinkled or have small puncture holes, and put out of service?

Answer.All your answers are in the MIL-B-81705C Standard document. Specifically, an Conductive shielding bag (type III) can be considered no good if it meets any of the following conditions:

the conductive bag delaminates as defined in section 4.8.4.1 in MIL-B-81705C

doesn't shield an ESD event under 30 kilovolts

has a static decay rate exceeding 2.0 seconds

does not attenuate EMI at least 10 dB

In general, a metallized shielding bag may still shield if it has crinkled or acquired small holes because of the Faraday affect, but it is safer to discard these bags and err on the conservative side. It would probably cost more to test and qualify the bag then to replace it.

Question. I have two questions about one material. Anti-stat bags.
1. How effective are anti-stat bags with a relative humidity of less than 20 % and temperatures as high as 110 degrees Fahrenheit.
2. How do you put a spec on an anti-stat (ohms/sq. etc.) bag to ensure maximum protection and re-use?

Answer.The clear static dissipative polyethylene (PE) that high quality vendors use in their bags is far superior than the "topically treated washed" pink poly products.

Dissipative and metallized shielding bags are made with volume loaded polyethylene which cannot be washed off and is inherent in the film. The PE resin that we use and all the additives are developed to minimize contamination.
Testing:
You could perform two test to ensure the proper operation of the bags:

1. perform a resistance test on the bag film to < 1x10^11 ohms @100 volts [using two five pound electrodes and megohmeter per esd s11.31-1994 and esd ds20.20-1998]
2. perform a tribocharge test, yielding static decay of less than or equal to 140 milliseconds, per FTMS 101C, Method 4046

Types of ESD Bags

Manufacturers also are developing more environmentally friendly materials than they had in the past. Historically, ESD protective packaging has environmental problems similar to any plastic material: disposal and material decomposition can present an environmental hazard. Recently, manufacturers have conquered some of the disposal problems, and we now see more recyclable ESD bags on the market, such as those made from polypropylene.

Let�s review the current technology for ESD bags. There are essentially three types or categories: conductive bags, dissipative bags and metallized bags. The latter two categories are typically the high-end of ESD bag product offerings and tend to have three combined properties of protection, (1) conductive, (2) dissipative and (3) shielding.

conductive Bags
conductive bags are typically coated with a topical antistat agent that helps minimize the generation of a static imbalance from triboelectric generation or contact and separation (i.e., definition of conductive). Some conductive bags are made with an antistat built into the films layers and tend to be more reliable and cleaner then the topically treated ones. A good bag has conductive properties on both the inside and outside of the bag�s film construction.

Dissipative Bags
Bags with the films surface resistance in the dissipative range are preferred because charge dissipates across the surface at a controlled rate. Most dissipative bags also have the property of being conductive. These are good general bags to be used in non-critical environments.

Shielding Bags
Shielding bags have either a metal film embedded into the bag film construction or coated onto an existing layer. This metal film acts as an electrical shield against electrical discharges from the outside of the bag. Depending on the energy and duration of the discharge and the thickness of the metal film, an ESD event is typically spread out over the outer surface of the metal film and if fully enclosed, i.e. the bag is sealed, then the charges current from the ESD event is contained to the outside of the metalic film allowing for a region of no electrostatic fields within the bag. This effect is known as the Faraday Cage Effect and is commonly used in controlling ESD via metallized shielding bags, conductive bags and the conductive tote box with a cover.